The invention concerns particularly though not exclusively, processes for the preparation of phosphorus-containing compounds useful in the preparation of catalyst compositions which facilitate the copolymerization of carbon monoxide with an olefinically unsaturated compound to make linear alternating copolymers.
Such copolymers and catalyst compositions are described, for example, in EP-A-121965 and EP-A-248483. To set the present invention in the context in which it was made these copolymers, catalysts, compositions and associated preparative process will now be described but it should be noted that many of the compounds and processes of the present invention, described in detail hereinafter, will be useful also in other contexts.
Broadly, such catalyst compositions comprise a Group VIII (in more modern nomenclature a Group 8, 9 or 10) metal. Examples of suitable Group VIII metals for use in such catalyst compositions are nickel and cobalt. However, the Group VIII metal is preferably a noble Group VIII metal, of which palladium is most preferred.
The Group VIII metal of such a composition is typically employed as a cationic species. As the source of Group VIII metal cations conveniently a Group VIII metal salt is used. Suitable salts include salts of mineral acids, such as sulphuric acid, nitric acid, phosphoric acid, perchloric acid and sulphonic acids, and organic salts, such as acetylacetonates. Preferably, a salt of a carboxylic acid is used, for example a carboxylic acid with up to 8 carbon items, such as acetic acid, trifluoroacetic acid, trichloroacetic acid, propionic acid and citric acid. Palladium(II) acetate and palladium(II)trifluoroacetate represent particularly preferred sources of palladium cations. Another suitable source of Group VIII metal cations is a compound of the Group VIII metal in its zero-valent state.
Such a catalyst composition is preferably based, as an additional component, on a ligand which forms a complex with the Group VIII metal. It would appear that the presence of two complexing sites in one ligand molecule significantly contributes to the activity of the catalysts. It is thus preferred to use a ligand containing at least two dentate groups which can complex with the Group VIII metal. Although less preferred, it is also possible to employ a monodentate ligand, i.e. a compound which contains a single dentate group which can complex with the Group VIII metal, in particular a dentate group of phosphorous. Suitably a bidentate ligand is used which contains two phosphorus-, nitrogen- or sulphur-containing dentate groups. It is also possible to use a mixed bidentate ligand such as 1-diphenylphosphino ethylthiopropane.